R. NICKBRYANMDS. JAMESZINREICHMD
The MRIs demonstrate a hyperintense intracanicular lesion on the left, consistent with a hemangioma. Rarely, hemangiomas appear in the cerebellopontine angle (CPA). They are usually small; the majority are 1 cm or less. They account for approximately 1% of CPA lesions.1 They have characteristic imaging findings depending on their location, either near the geniculate ganglion (GG) or in the IAC. For the former, hemangiomas arising from the perigeniculate capillary plexus, computed tomograms may show a smooth enlargement of the GG and enlargement of the labyrinth portion of the fallopian canal by a soft tissue mass. Although they do enhance, this finding is subtle, owing to the tumor's size. Other CT findings include "honeycomb bone," irregular and indistinct bone margins, and intratumoral bone spicules and calcium. The size and the irregular bone margins help to differentiate hemangiomas of the IAC from seventh nerve schwannomas, which are larger and produce sharp bone margins.2 Magnetic resonance imaging studies may also help, showing heterogeneous signal intensity that may reflect these bone changes. However, MRI studies without gadolinium are reported to miss 60% of GG vascular tumors.3 Therefore, high-resolution CT may be the diagnostic study of choice for GG lesions, because this imaging modality can best pick up the bony changes. However, hemangiomas that form in the IAC, like the one in this case, are more reliably demonstrated by MRI than GG lesions. On CT scans, hemangiomas appear nearly identical to an acoustic neuroma. However, on MRI scans, IAC hemangiomas produce a more hyperintense signal than acoustic tumors,3- 7 but since they bear so much resemblance to acoustic neuromas, they are typically not diagnosed until surgery.
Imaging Quiz Case 2. Arch Otolaryngol Head Neck Surg. 1998;124(7):818. doi:10.1001/archotol.124.7.814